Fragile X Syndrome

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Fragile X syndrome affects a child's learning, behavior, appearance, and health. Symptoms can be mild or more severe. Boys often have a more serious form of it than girls.

Children who are born with this genetic condition can get special education and therapy to help them learn and develop like other kids. Medicines and other treatments can improve their behavior and physical symptoms.

What Causes It?

The FMR1 gene, which is on the X chromosome, makes a protein called FMR that helps nerve cells talk to one another. A child needs this protein for his brain to develop normally. Children with fragile X make too little or none of it.

People with this condition also have more copies than usual of a DNA segment known as CGG. In most people, this segment repeats five to 40 times. In people with fragile X, it repeats more than 200 times. The more times this DNA segment repeats, the more serious the symptoms are.

A mother with the FMR1 gene change has a 50% chance of passing it to any of her children. A father can only pass it to his daughters.

Boys are more likely to have fragile X than girls, and they have more severe symptoms. This is because girls have two copies of the X chromosome. Even if one X chromosome has the gene change, the other copy can be fine. Boys have one X and one Y chromosome. If the X chromosome has the gene change, they will have symptoms of fragile X syndrome.

Some people inherit the fragile X gene without having symptoms. They are called carriers. Carriers can pass the gene change to their children.

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How Is It Diagnosed?

These tests can be done during pregnancy to see if an unborn baby has fragile X: